There have been mainly used plastic cards with a magnetic tape adhered thereon as represented by credit cards in settlement for payment of prices or fees for commodities and services, and when settlement to be made, an individual is identified by having a card reader read information on the individual stored in the magnetic tape and verifying the read information to data specific to the managing business organization. Recently, criminal acts such as falsification of cards frequently occur, however, and the use of IC cards which can hardly be falsified has been becoming more and more frequent.
The electronic settlement making use of online authentication also has been put into practical use, and in addition to the use of credit cards, various efforts for making it harder to decode a card number have been made by enhancing the security based on combined use of the encryption technology and personal identification numbers. An IC card has a substantially larger capacity for information storage as compared to the conventional types of cards, and its portability is excellent, but the user's awareness of carrying the IC card is rather weak, and is still at the level as indicated by the expression of “Probably it's in my wallet/purse”. A credit card is often put in a wallet/purse, and therefore there is the risk that it may be stolen or lost.
Recently cellular phones are very popular, and while their portability is lower than that of credit cards, the users are well aware that they have the cellular phones with them. In addition, the cellular phone hardly becomes an object for theft because it is not well adapted to be used by a third party, and therefore electronic settlement systems based on use of cellular phones have been developed.
There has been well known the method in which, after a user order from a commodity by using a cellular phone, the user calls the settlement server, then inputs key information such as a credit card number or the like, and performs settlement with the credit card. In this electronic settlement method, when key information such as a credit number is transmitted or received, the Internet where the risk of illegal use of stolen data is high is not utilized, and therefore the voice communication mode is used and information is transmitted by operating the push buttons. The transmitted information by operating the push buttons is encrypted, but the information is still not sufficiently secured.